Hmm not sure. That bug that you linked to is quite old though.
Now that I read your post again, it looks like you're looking for a definition of what the domain admin can do? The current capabilities can be found in their wiki:
Administration Console - Zimbra :: Wiki It looks like they can manage Accounts, Aliases, Distribution Lists, and Resources. The wiki page says the specific functions are explained in the help files. Your domain admins should be able to set quotas up to a limit that's set by a system administrator. I know that they can't use the 'view mail' button.
Going forward, it looks like the delegated domain administrator in Zimbra 6.0 can only manage other domains with the same capabilities as now. I could be wrong though.. I've only installed the 6.0 beta of the open source version, not the NE version.